ANKARA--Turkey said on Tuesday it had agreed with the United States on terms for setting up a "safe zone" inside northern Syria as part of their campaign against Islamic State militants, but the U.S. State Department denied there was any such agreement. The two NATO allies have been working on plans to provide air cover for Syrian rebels and to sweep Islamic State from land along the Turkish border. CNN Turk quoted Turkish foreign ministry undersecretary Feridun Sinirlioglu as saying the countries had agreed to create a 98 km (61 miles) long and 45 km wide area to be patrolled by members of the opposition Free Syrian Army. In a later statement, Turkey's foreign ministry quoted Sinirlioglu as saying: "The control and protection of this region cleared of (Islamic State) will be conducted by Syrian opposition forces and the necessary air defence and support for this ... will be provided by the United States and Turkey." Asked about the report, however, U.S. State Department Mark Toner said: "There's no agreement on some kind of zone." Toner said he had not seen the Turkish official's remarks and could not address them. "I'm not denying his claims," he added. "We've been pretty clear from the podium and elsewhere saying there's no zone, no safe haven, we're not talking about that here. What we're talking about is a sustained effort to drive ISIL out of the region," Toner told a news briefing. ISIL is another name for Islamic State, which has seized large swathes of land in both Syria and Iraq. Under the Turkish-U.S. strategy, moderate Syrian rebels, trained by the U.S. Army, will fight the Islamist militant group on the ground and help coordinate air strikes by the U.S. coalition, launched from Turkish air bases. U.S. and Turkish forces would hit Islamic State or Kurdish militants if they entered the safe zone, CNN Turk quoted Sinirlioglu as saying. Diplomats familiar with Ankara's plans have said cutting off one of Islamic State's lifelines could be a game-changer in this corner of Syria's complex war. The core of the U.S.-trained rebels, who number fewer than 60, will be highly equipped and be able to call in close air support when needed, they say. U.S. officials have previously said discussions are ongoing about the size and scope of a safe zone along the border, but that the aim would be to clear it of Islamic State fighters and allow moderate rebels to operate freely. They have ruled out a formal no-fly zone.